In the construction of concrete building foundations, roadways, support members and the like, particularly those having steel reinforcing, it is often necessary to pour different portions of the concrete at different times, or to connect a new concrete wall or foundation to an older structure. In such cases, the second concrete portion abuts against the surface of the first pour. In both new and old constructions, ambient temperature fluctuations inevitably cause increases or decreases in concrete volume and consequent changes in the joint openings. As new concrete dries, it also sets and shrinks relative to the previously-poured concrete leaving a crack or space through which water can travel.
In order to prevent the unwanted passage of water through abutting joints of concrete, it is well known to use one or more waterstops in order to seal the various concrete joints in the foundation. An early variety of such waterstops used copper and steel plates in cooperative engagement between adjacent slabs. More recent waterstop designs consist of sealing elements made of an elastic deformable material with or without integral elastic and/or metal anchoring portions which are installed in the newly-poured concrete to seal the joints.
Concrete foundations for large water reservoirs or water storage tanks are often poured using a plurality of adjacent concrete slabs separated by one or more different types of waterstop constructions. Large concrete support structures, building floors and the like are also poured in sections or "panels" with expansion joints and/or waterstops dispersed throughout the structure. Certain waterstops (typically referred to as "expansion-type") are specifically intended to seal the concrete joints while at the same time permitting expansion and contraction of the adjacent panels. Other "labyrinth" type constructions are not used in applications requiring thermal expansion and contraction. Nevertheless, the present invention relates to both categories of previously-installed waterstop devices.
In prior art constructions, waterstops of elastic material are generally characterized as "passive" in nature. A typical passive waterstop design is illustrated in U.S. Pat. No. 3,172,237 and consists of a flat strip of elastic material which is partially embedded in the first concrete pour and projects outwardly from one end of the concrete. Usually, in order to install such waterstops, the form for the concrete must contain a longitudinal slit along one end to allow the flat strip portion of the waterstop to project outwardly. The concrete for the second section is then poured with the projecting portion embedded in the new concrete.
Most conventional waterstop designs use anchoring means in the form of ribs or the like along their edges to ensure proper anchoring in the adjacent panel sections. Often, however, during the second pour, the projecting portion of the strip becomes flattened and/or displaced from its proper position and thus will not be properly anchored in the new concrete. Ultimately, poor anchoring results in failure or the propagation of cracks at or near the waterstop which then permit water to seep through the joint foundation. For certain water storage facilities, such as a water tank for a large metropolitan community, even a small amount of leakage through a failed or damaged waterstop can result in substantial water losses or the contamination of potable water in ground water sources over a period of time. Further, the repair of such waterstops generally requires that the entire facility be taken out of service to perform the necessary repairs to the foundation.
One distinct disadvantage of conventional waterstop constructions is that the newly-poured concrete panels shrink during curing, thereby causing the embedded flanges to pull away from the surrounding concrete matrix. As a result, the flanges of prior waterstops often become loose before the concrete panels are completely set. Even after installation, the repeated expansion and contraction of adjacent panels of concrete (due to ambient temperature fluctuations) causes the embedded flanges to loosen to the point they permit water to flow around their edges.
Thus, the principal problem encountered with passive (expansion-type) waterstop devices is that they do no adequately provide for shearing movement--that is, relative lateral motion between adjacent panels or between the floor and side walls of structures due to unequal exposure to extremes of temperature. The latter situation exists, for example, in the case of a concrete storage tank where expansion and contraction of the concrete side walls due to changes in temperature result in expansion and contraction of the diameter of the tank, but no comparable change in the floor or footings on which the walls rest. Even when properly installed, conventional waterstops may not effectively accommodate the shearing forces which exist within the structure simply because the two faces of the waterstop are anchored to different concrete panels. Such problems in anchoring are particularly acute for joints at the corners and angled intersections between panels which require matching waterstop configurations. During normal expansion and contraction, the waterstop may be subjected to severe shearing stresses along the intermediate portion between concrete sections, resulting in cracks or failure of the waterstop even before the foundation is completed. After installation, the waterstops are subjected to constant expansion and contraction and, under normal conditions, the "bulb type" elastic material may become over-extended and tear, or the anchor portions may become dislodged or fail completely. In addition, over an extended period of time, the contact pressure between the anchors and the concrete may leave a large potential area of leakage, especially in regions where the waterstop is embedded in an imperfect concrete matrix.
In applications in which the concrete joints are subjected to outside water pressure (such as tunnels or enclosed chambers), debris and solid particulates may penetrate the joint and eventually contribute to the leakage and/or distortion of the waterstop in its installed position. Even when new waterstops are installed, care must be taken not to permit debris or foreign materials to fall into the concrete joint since their presence may cause the waterstop to fail.
The installation of bulb type waterstops is also cumbersome and costly. As indicated above, the conventional practice for installing such waterstops requires that the mold form be split or, alternatively, that the form be recessed to accommodate the non-embedded-portion of the waterstop. In either case, the procedure is expensive and time consuming, primarily because the joint is totally inaccessible for repair without removing or dismantling the entire concrete structure. Thus, it is essential that a waterstop in a newly-installed structure perform satisfactorily, particularly "expansion"-type waterstops which must accommodate the shearing forces between adjacent joints.
A number of prior methods have attempted to repair existing waterstops. For example, sealants, such as epoxy gels or elastomeric compounds have been used to seal joints between construction panels or slabs of concrete in order to make the joint "waterproof". Generally, the sealant has been applied by injection between adjacent concrete slabs and then coating the joint with a tape or sheeting material. However, such sealing techniques have not been satisfactory primarily because the sealants are highly sensitive to moisture and require very dry surface conditions to ensure proper adhesion over the joint area. Also, the repair procedure is time consuming and expensive and does not provide a permanent water-tight seal capable of handling head pressure or the normal expansion and contraction of adjacent panels.
The known repair methods of injection are also ineffective for preventing the propagation of leaks in foundations which are subjected to hydrostatic pressures over prolonged periods of time such as, for example, a water storage vessel. In addition, the conventional methods of repair cannot be used for water storage facilities in which the concrete joint is subjected to both positive and negative water pressure, i.e., head pressure on one or both sides of the joint. "Negative" head pressures exist when the water pressure on one side of a concrete joint is greater than on the other side. If the waterstop is subjected to pressure on one side, it tends to "balloon out" in one direction over a period of time and thereafter will not effectively prevent leakage due to pressure on the opposite side. In other cases using the conventional sealant repair technique, care must be exercised not to smear the sealant on adjacent surfaces of the concrete. Thus, an additional time consuming procedure of masking the adjacent surfaces may be required.
Other repair techniques use a modified form of expansion joints in order to minimize the effects caused by thermal expansion and contraction. Often, a bituminous material will be injected or positioned in the slot between the concrete slabs. Invariably, however, foreign matter, such as dirt, small rocks, water and the like, become lodged in the crack and tend to loosen the joint due to cycles of expansion and contraction. Another disadvantage of bituminous materials is that they are not flexible and, during normal expansion and contraction, cause the cracks to fill with extraneous material resulting in additional unwanted expansion and/or water leakage.